Lithium ion nonaqueous electrolyte batteries are widely used as high energy density batteries in a variety of fields such as electric vehicles, electric power storage, and information instruments. Accordingly, market demands on nonaqueous electrolyte batteries are further growing, and active studies are being made.
Among them, nonaqueous electrolyte batteries as a power source for electric vehicles are demanded to have a high energy density, or a high discharge capacity per unit weight or unit volume.
On the other hand, with the increase of the discharge capacity per unit weight or unit volume of a nonaqueous electrolyte battery, the demand for safety also increases. One of the resolutions for the demand is an all-solid-state secondary battery.
An all-solid-state secondary battery is a secondary battery including a solid electrolyte in place of a liquid nonaqueous electrolyte, more specifically a liquid organic electrolyte. Since liquid organic electrolytes are ignitable, techniques for improving safety of batteries including a liquid organic electrolyte are actively developed. However, it is still difficult to secure sufficient safety.
On the other hand, all solid secondary batteries include no liquid organic electrolyte, and thus carry an extremely low risk of ignition, and exhibit extremely high safety.
Furthermore, all-solid-state secondary batteries include no liquid electrolyte, which allows the use of an electrode having a bipolar structure. An electrode having the bipolar structure is obtained by providing a positive electrode on one surface of the current collector, and providing a negative electrode on another surface of the current collector. Furthermore, a bipolar battery is suitably formed by providing a solid electrolyte layer on each surface of the positive and negative electrodes, and stacking plural electrodes having the bipolar structure in such a manner that the positive and negative electrodes are opposed to each other, with a solid electrolyte layer or collector sandwiched therebetween. In this bipolar battery, the increase of the number of stacking allows the increase of the voltage in the battery.